Structural openings in the walls of commercial and residential buildings include openings provided to enable the installation of doors, windows, passageways and recessed areas for bookcases, shelves, niches and the like. The framing of such openings during building construction allows sufficient space to enable precise positioning, adjustment and final alignment, then fastening of doors, windows and other elements during installation. Door and window units come in standardized sizes to simplify the installation processes, and are often provided with attached frames that simplify the installation of such units into framed structural openings. However, when such units are installed into structural openings, permanent gaps often appear between the structural framework and the abutting surfaces of the frames surrounding the units as a consequence of precise vertical and horizontal alignment of the units within, and fastening to, the structural openings.
It is common construction practice to cover the gaps between the framework of structural openings and installed units with trim mouldings, also commonly known and referred to hereinafter as casings. These are usually elongated relatively thin flat pieces of trim bounded by elongated linear side edges and shorter linear end edges. It is also common practice to have decorative profiles cut into at least one linear edge of casing pieces to enhance the visual appeal of the casings. Such decorative profiles can be simple or complex depending on the type of aesthetically pleasing appearance desired. The process of cutting decorative profiles into the edges of casing pieces is commonly known as milling.
Casing pieces with aesthetically pleasing decorative profiles milled into their linear edges are often used to construct other decorative elements in commercial and residential structures. Such decorative elements include chair railings, wainscoting, borders around the perimeters of walls and ceilings, and the like. However, installation of casings to conceal the gaps between installed units and the framework of structural openings, and to produce other decorative design elements on walls and ceilings, is time consuming and requires considerable skill and precision to achieve aesthetically pleasing results.
There are two common methods for installation of casings. The first method involves fitting together the individual vertical and horizontal casing pieces surrounding a structural opening by means of mitre joints wherein each end of a casing piece is cut precisely at a 45° angle to enable the formation of a tightly fitted and squared 90° corner. If the end-cuts are not precisely made with 45° angles, then visually displeasing small gaps will result in the mitred corners that join the vertical and horizontal casing pieces. In these cases, even more construction time is required to fill the gaps with a suitable putty or other filling compound, to allow the filling compound to harden, and then to remove excess filling compound by sanding to eliminate the gaps. As the complexity of the design milled into the linear edge of casing pieces increases, the difficulty of precisely cutting and fitting mitred corners is increased.
The second method involves installation of square blocks at the top corners around units such as doors and windows in a manner that bridges the gap between the units and the framework of the structural openings. The ends of the individual horizontal and vertical casing pieces are cut at precise 90° angles and are then tightly butted against the corner blocks. However, the second method is also time-consuming and requires considerable skill and precision to ensure that the corner blocks are perfectly squared and vertically aligned. Misalignment or un-squared corners will result in aesthetically unappealing gaps between the casing pieces and corner blocks. These gaps must also be filled with an appropriate filling compound that has been sanded after it has hardened.
An additional problem encountered when installing decorative casing pieces is that of joining vertical and horizontal casings which have different decorative profiles milled into their edges. One example of such a situation is the joining of a vertical casing piece to a horizontal casing piece installed in a vertical orientation at the juncture of a wall with a floor. In these situations, the decorative profile milled into the linear edge of one casing piece must be traced onto a paper pattern that is then transferred to the receiving edge of a casing piece with a different decorative profile milled into its linear edge. The first decorative profile is then cut into the second decorative profile by means of a coping saw. This process requires considerable skill, precision, time and patience in order to produce tightly fitting joints between adjoining casing pieces.
Because of their decorative properties, casings are also commonly used for installation of aesthetically appealing chair rails, wainscoting and other decorative elements on walls and ceilings. The vertical and horizontal casing pieces used to create such decorative trim work are abutted and joined by means of mitre joints. Consequently, the installation process for casing pieces used for decorative trim work is also time consuming and requires skill, precision and patience to produce tightly fitting squared joints.
There is therefore a need for an improved system for assembling and installing casing pieces that avoids at least some of the problems indicated above.